This invention relates generally to catamaran type boats, and more particularly to improvements in the structure or structures that support the main hulls of such boats on pontoons.
In a catamaran boat, the main hull is normally positioned above the water surface, and carries a support means for carrying the pontoons. The main hull provides accommodation for passengers, and is located above the water surface to minimize motion and spray due to the action of waves. In this regard, the primary goal of a PLANING SWATH boat, which is the generic name for this new concept, is to minimize motion at both pre-planing and at planing speeds. Motion is reduced by two laterally-spaced pontoons which are mounted below a main hull by support means. The pontoons are at least mostly submerged at pre-planing speeds, and rise to plane on the water surface at higher speeds.
"SWATH" is an acronym for "Small Waterplane Area Twin Hull" which stems from its use for a displacement-type of ship known as a SWATH ship. A PLANING SWATH is similar to a SWATH ship, except that its pontoons are designed to plane on the water surface instead of always remaining submerged. This distinction permits a PLANING SWATH to reach much higher speeds than a SWATH ship.
The main hull structurally ties together the two laterally-spaced pontoons and their associated support means. At rest, and at pre-planing speeds, waves can produce large side loads on the pontoons and their support means. These side loads produce large transverse bending moments on the main hull. Consequently, the main hull must have structural means for handling these bending moments. Typical means consist of lateral frames, bulkheads, or box beams.
Other large loads applied to the main hull are upward forces produced by waves impacting the pontoons and support means. These loads can be highly asymmetrical, thereby producing large torsional forces on the main hull, for example certain wave conditions that try to trim one pontoon upward while trying to trim the other pontoon downward.
The lower deck of the main hull is exposed to downward loads from people and equipment, and upward loads from wave impacts.